A conventional domestic fan typically includes a set of blades or vanes mounted for rotation about an axis, and drive apparatus for rotating the set of blades to generate an air flow. The movement and circulation of the air flow creates a ‘wind chill’ or breeze and, as a result, the user experiences a cooling effect as heat is dissipated through convection and evaporation.
Such fans are available in a variety of sizes and shapes. For example, a ceiling fan can be at least 1 m in diameter, and is usually mounted in a suspended manner from the ceiling to provide a downward flow of air to cool a room. On the other hand, desk fans are often around 30 cm in diameter, and are usually free standing and portable. Floor-standing pedestal fans generally comprise a height adjustable pedestal supporting the drive apparatus and the set of blades for generating an air flow, usually in the range from 300 to 500 l/s. The pedestal may also support a mechanism for oscillating the drive apparatus and the set of blades to sweep the air flow over an arc.
A disadvantage of this type of arrangement is that the air flow produced by the rotating blades of the fan is generally not uniform. This is due to variations across the blade surface or across the outward facing surface of the fan. The extent of these variations can vary from product to product and even from one individual fan machine to another.
These variations result in the generation of an uneven or ‘choppy’ air flow which can be felt as a series of pulses of air and which can be uncomfortable for a user.
In a domestic environment it is undesirable for parts of the appliance to project outwardly, or for a user to be able to touch any moving parts, such as the blades. Pedestal fans tend to have a cage surrounding the blades to prevent injury from contact with the rotating blades, but such caged parts can be difficult to clean. Furthermore, due to the mounting of the drive apparatus and the rotary blades on the top of the pedestal, the centre of gravity of a pedestal fan is usually located towards the top of the pedestal. This can render the pedestal fan prone to falling if accidentally knocked unless the pedestal is provided with a relatively wide or heavy base, which may be undesirable for a user.